Micromirror unit and method of making the same

A method of making a micromirror unit, the unit comprising a mirror forming base, an inner frame surrounding the mirror forming base, an outer frame surrounding the inner frame, first torsion bars connecting the mirror forming base to the inner frame, and second torsion bars connecting the inner frame to the outer frame, the method comprising the steps of:

• preparing a substrate which includes a first conductive layer, a second conductive layer, and an intermediate insulating layer interposed between the first and second conductive layers;
• etching the first conductive layer of the substrate in a manner such that material removal from the first conductive layer terminates short of the insulating layer at portions corresponding to the first and second torsion bars while reaching the insulating layer at selected portions other than the first and second torsion bars;
• etching the second conductive layer in a manner such that material removal from the second conductive layer terminates short of the insulating layer at portions corresponding to the second torsion bars while reaching the insulating layer at portions corresponding to the first torsion bars and at other selected portions excepting the second torsion bars;
• and
• etching away the insulating layer at the first torsion bars and at other selected portions excepting the second torsion bars.